Slotted winged cylindrical antenna



Sept- 23 1952 A. ALFORD SLOTTED WINGED CYLINDRICAL ANTENNA Filed June 14, 1948 4 Sheets-Sheet l Mmmm lTllllllIlIlllll lllllllllllllllllll l .I

IN VEN TOR.

M ,W A w Sep't. 23, 1952 A; ALFQRD 2,611,864

SLOTTED WINGED CYLINDRICAL ANTENNA Filed June 14, 1948 4 Sheets-Sheet 5 Sept. 23, 1952 A. ALF-'ORD SLOTTED WINGED CYLINDRICAL ANTENNA Filed June 14, 1948 4 Sheets-Sheet 4 IN VEN TOR.

Bijna/Pew lfom/ uw @my Patented Sept. 23, 1952 ori-ics y Anfaenger y sLoT'rEp WINGED oYLINDaroAL ANTENNA n Cambridge, lVlassv. Application Junell, 1948. Serial No. 32,752 (Cl. Z50-3,3)

v 12,. Claims. 1

The present invention relates .to ultra,high y frequency radio antennas with a directional pat-` n tern in'which the backward radiation in a polar diagram pattern has a decreased radiation as compared to the forward sector overa desired sector of arc.

In the present invention one of the' desired types of patterns produced is that'oi'a cardioid having a very low radiation over a wide. cycle of backward directions, the, backward directionin the present invention referring to the sector of arc in the polar diagram where the radiation is least. According to the present invention the center of this sector may have a verylow radiation for some 40 or less,v increasing gradually to auniform constant amplitude of radiation in the forward sector. 1 Y, :k L

The present invention is particularly useful and applicable for television broadcastsl under conditions Where two cities such asA andB some fty miles apart both have stations operating on channels adjacent to each other. If, for ins-tance, city A has several television stations and all channels which can be assigned to city B; without resulting in' interference with stations in cityv A' have been assigned, `the system of the Vpresent invention will make it possible by use of directional antenna according to the present invention to assign an adjacent channel tothe station at city B so that operation without interference can be effected. For example: channel 9 can be used in city B in spite of the factv that channels 8 and 10 are already assigned and used in city A.

In the present invention a slotted cylinder with metallic wings is preferably used. This type of antenna alone has alradiation pattern of the desired shape in a forward direction but fails in the backward sector which normally is only about 1 0 db below the maximum in the forward direction. The desired pattern requirements for the back lobe should be about 35 db below the maximum so that the slotted cylinder with the metal,- lic wings will not alone suiiice. If a large metal sheet is placed inback of the wings of the an@ tenna, some supression of the back lobe is obtained. However the amount of suppression does not appear suicient and in addition to this, the

size of the sheet would necessitate additional' structural support comparable in size for the antenna proper. As contrasted with this arrangement the one of the present invention employs two auxiliary driven elements in addition to the main driven antenna with proper adjustment of amplitude and phase for the auxiliary driven elements so that the total radiation directly backv virtual sources.

ence is a half wave length.` At this angle there is, .a null. At an angle greater than to the totaleld radiate in all directions.

wards is reduced to thedesired low value.v Ak consideration of the slotted cylindrical antenna with outwardly: extendingl wings .shows that thel voltage across the slot originates a wave which travels outward along the wings in a direction .perpendicular to the cylinder and that when the wavela'rrives at the edge of the wing,.some of the energy is reflected back towards the slot and some travels around the, edge in such a way as to keep the f ends of the electrical lines of force normal to the plane of the wings. The energy which travels arcundthe edge oi the wingsl causes. the: back lobe'. The eld configuration nearithe'edges can beV considered as two Huygens sources which- The amplitude and phase of these sources are dependent on the width of the wing. If the structurefis symmetrical, the

two Huygens sources are in the same phasewithl each other and their contribution Jaddi'n the dif. rection of 180 that is in the backward direction bisecting the angle between the `two wings. At a deviation angle from 180 there is a difference in path length between the radiations from these At an angle o this pathdifierincreases. As angle approaches the iield of the main slot becomes predominantwith the smaller eiiect ofthe two edges superimposed;

` The angles may be assumed to be 'areference angle deviating from the ,line yby virtue'of the characteristics of the antenna-.for desired conditions and therefore are notv shown on the drawings. v v n `On the basis of the above discussion,` it would follow that the proper place to locate the auxilif; ary radiators is at or near the edges of the wings.v If a low signal is to be obtained over as widerfan.v angle as possible, the combined patternV of the two cancelling elements should track the pattern,

of the Huygens sources as closely. as, possible. This can be accomplished when the'spacing between the two cancelling elementsv ismade equal to the eiective electrical spacing of the Huygens sources. Then, if the cancelling elements are fed so as to produce the eld of the same ampli'-y tude as` that in the back lobe, butv in rreversed Y phase,. it would be expected that the field inthe rear drop to vary low values over a wide angle. ,l

It will be noted from the discussion in the specication below, the position of the auxiliary radi-A ators is critical if a substantial reduction in the back lobefor a wide sector is desired. The aperably greater than the physical spacing between 3 the outward edges of the wings. It is therefore necessary for an effective reduced back radiation to position the rear cylinders beyond the edge of the wings. Various methods of feeding the antenna of the present invention may be employed and the structure may comprise a number of repeated sections depending upon the power which the antenna is to handle.

.The present invention will be more fully described and the principles of its operation more fully analyzed and explained in the specification below when taken in connection with the drawings illustrating an embodiment of the same, in which:

Figure 1 shows a simplified. form of the antenna structure alone as viewed from a front elevation in which the greater portion of the radiation isv directed.

Figure 2 shows a rear elevation of the antenna of Figure 1.

Figure 3 shows a plan view of from the top.

Figure 4 shows a plurality of antennae of Fig:- urefl employing a slot with closed ends in a ver'- Figure 2 as viewed tical array.

The general arrangement of the antenna will be seen from the drawings. Referring more particularly to Figures 1, 2 and 3, it will be noted thatthe main unit consists of a conducting cylinder I having a gap 2 with conducting side-wings 3 and 4 extending tangentially from the cylinder near the gap at an angle slightly backwards from` the. horizontal. Taking the line B of symmetry backwards as 180 in a. backward direction, the angle A to the wines may be approximately 70.

Thezcylinder I may vary `in shape from that of' apure cylinder in the generalmanner that has.

been previously pointed yout in some of4 my prior applications, referring particularly tc my appli-v` cation Serial No. 694,319, filed August 31,1946'. Suchvariations may include figures symmetrical about-acentral axis and iigures havingi an axis offsymmetry with the plane. The size of' the cylinder andthe size of the wings may vary of course with the operating frequency andV in 'general the lower thefrequency the larger willbe the dimension of the antenna. radiators may comprise cylinders 5f and Gof'the same general design as cylinder I. rIhese are provided withair. or insulated gaps. 'I and 8; respectively whicliface backward'. in the directiony of the axis B. The. cylinders are positioned in the vicinityk of the outer edges of th'ezwings.. If: thewings 3 and 4L are continued: the cylinderswill. preferably be tangential to' the planes of the.

wings a short distance beyond the normal wing lengths in most cases. These slots are. usually covered with a sheet of insulating material to keep The reason for this will be explained? In the use of an open or insulated antenna.` slotsuch as shown inFigures 1, 2and .3, .the-.1an-k out ice. later.

The auxiliary track only .over an angle of about 20.

value. of. field whichas indicatedis 690mm tenna may be fed at one end by coaxial cables 9,

- I0 and II as indicated. The inner conductor of the cable is'connected to one side of the gap and the outer conductor is connected to the other side of the gap. To the main cylinder I is fed the major portion of the power and to the auxiliary cylinders 5 and 6 is fed an auxiliary current whose phase and amplitude will be adjusted to produce the desired annulling or compensating eiect to reduce the backward rotation pattern as will be presently indicated.

In the arrangement indicated in Figure 4 where a group of two units are used as is indicated by I2, I 3. the cylinder slots I5, I6 and I1 are shown as closed and slots and may therefore be fed by a feed at the center from coaxial cables I9, I9', 20, 2D vand 2I, 2I. Means I4 are provided for adjusting the phase and relative amplitude fed to the auxiliary cylinders while the main cylinders are fed through the cable 40 connected to the junction` box 4I from which cables 20 and 20' lead;

An insight into the positionv of the'. auxiliary cylinders. isv shown by thek curves' of Figures and 8.v

The pattern of Figure 7 was obtained with a model antenna operating at 2,000 mc'. The two slotted cylindersin thisL case were fastened to the backside of the Wings with the slots facing to the rear and allV three cylinder' elements were driven with the tworearcylindersproperly adjusted toV give a minimum' of radiation at 180. The nullindicated in Figure'? by the dotted-line curve `in the polar diagram is deep but does not extend. over as large an angle. asV is desired. The reason for this diiculty becomes. clear Aon an examination of Figure 8. In this iigure the curve 22 is the pattern of the front cylinder' with the wings, while thedotted curve 23 is the pattern of the two auxiliary rear cylinders fed independently of the front cylinder. The two patterns' A closer examination, as has been` stated above, shows that the .apparent spacing. of the Huygers source'si'is considerably greater thanV the physical spacing ofthe two rear cylinders in this arrangement.. The; effective phase. centers ofA the, Huygens sources are not attheedgesof the wingsbut are beyond them.

As contrastedrwith the curves ofFiguresfand- 8,.the-curves ofi'figures; 5 and 6`show'al more de#-` sirable pattern-in the. polar diagram ofi` Figure 6 whichrcorresponds ingeneral. to the preferable arrangementof Figure 3: The pattern 25` is for theffront cylinderwiththe wingsrand the pattern 2E' is for the rear. cylinders.' It is'clearA that the tracking inzthe .rear sector of the1pattern-is quite close over-a wide: angle. In. Figure 5 a'curve is shown with a plot of relative .amplitudes as ordinatesand the' azimuth. directions plotted as aliscissae. The dotted curve `30 representsthedesired protection in'rthe desiredasector..

defined-in the table-below basedon anR.A M.

TABLE [RL-Mi S. value of 'l'd'69'0 niv] A Ampere i. E-mv.

20 2D 30 so.V 2255 This is ai curve based on normal requirements. and ,iss,.

The curve 3| shows the back sector radiation corresponding to the curve taken in Figure 6 and shows substantial compliance with 4the desired pattern. In Figure 5 the minimum amplitude of back direction occurs at approximately 12 on either side of 180.

The'relative power for the main andauxiliary.

cylinders may be obtained from the curves -of Figure 6. The amplitudes of the two patterns in Figure 6 are adjusted so that they are equal at 180. By integrating the two patterns it is found that the two rear cylinders together require'J/; as much power as the main cylinder.

in opposite phase to that of themain cylinder. Since the presence of the auxiliary vcylinders in the eld causes some irregularities in the vradiation from the wing edges it is not too practical to determine the position of the auxiliary cylinders Wholly by calculation. Experimental patterns should be obtained on a model at correspondingly high frequency, to determine the position of the cylinders more exactly for the desired pattern of radiation.

The relative dimension given in Figure 3 we obtained by such experimental procedure and may, therefore, be used. It should be added that when great accuracy of pattern is desired the effect of relatively small llings located in the field of the radiation may become appreciable so that care in engineering design is necessary.

Having described my invention I now claim:

1. An ultra high frequency antenna comprising a main unit formed as a conducting cylinder having a slot extending longitudinally thereofv allel to the axis of the slotted cylinder positioned near but beyond the ends of said wings in positions equal to the effectivev electrical spacingv of the Huygens sources from said slot, and means for feeding said auxiliary conducting units for' producing fields of substantially the same vamplitudes in reversed phase as said Huygens radiation sources, whereby a composite radiation pattern substantially of a cardioid figure with a null in the direction of diametrical symmetry of the antenna will be obtained.

2. An arrangement as in claim 1 in which said auxiliary conducting units comprise a pair of conducting cylinders each having a slot extending longitudinally thereof.

3. An arrangement as in claim 1 in which said main unit has its slot electrically shorted at both ends.

4. An arrangement as in claim 2 in which said main and auxiliary units have their slots electrically shorted at both ends.

5. An arrangement as in claim 2 in which the slots in the auxiliary cylinders face in the opposite direction from the slot in the main cylinder.

The rear cylinders therefore will be energized in this ratio Cil 6. An ultra high frequency antenna comprising a main unit formed as a conducting cylinder having a closed ended slot extending parallel to the axis thereof with outwardly and backwardly extending conducting wings extending from the outer surface of thecylinder at each side of said slot, having a diametrical axis of symmetry through the axis of said cylinder, a pair of auxiliary cylinders positioned beyond the ends of the wings, each auxiliary cylinder having a closed ended slot parallel to the axis thereof and to each other and the main cylinder, the slot of the .main cylinder facing forward of the wings and the slots of the auxiliary cylinders facing backward.

'7. An arrangement as in claim 6 including means for feeding said cylinders across the slots.

8. An arrangement as in claim 6 including means for feeding said cylinders across the ends of the slots therein.

9. An arrangement as in claim 6 including means for feeding said cylinders across the middle of the slots therein. l

10. An arrangement as in claim 6 including means for feeding the main cylinder and the auxiliary cylinders separately, the latter with a fraction of the power supplied to the main cylinder in the reverse phase for substantially annulling a part of the backward lobe produced by the main cylinder alone.

11. An arrangement as in claim 6 including means for feeding the main cylinderr and the auxiliary cylinders separately, the latter with a fraction of the power supplied to the main cylinder in the reverse phase for producing a composite radiation pattern substantially of a cardioid figure with a null in the direction of the diametrical symmetry of the antenna.

12. An arrangement as in claim 6 inv which the cylinders and wings reoccur in repeated sections with corresponding elements in substantial alignment and means for feeding each of said cylin ders with ultra high frequency.

ANDREW ALFORD.

REFERENCES CITED` The following references are of record in the le of this patent:

UNITED STATES PATENTS OTHER REFERENCES Radio, July 1946; pages 14 and 15. Electronics, September 1948; pages 103 to 107. Proceeding of IRE, Patterns of Slotted-Cylinder Antennas, by George Sinclair, December 1948;

pages 1487 to 1492. 

